title: Potential mortality effects of off-highway vehicles on the flat-tailed horned lizard (Phrynosoma mcallii): a manipulative experiment.
abstract: Southern California desert public lands receive especially high levels of off-highway recreation due to large population centers nearby and popular riding environments such as sand dunes. Controversy has developed over the flat-tailed horned lizard (Phrynosoma mcallii), previously a candidate for listing under the Endangered Species Act. Some evidence suggests lower lizard abundance in areas of higher recreational use than in areas with low or no use. We designed a manipulative experiment to ensure maximum inference in evaluating the direct impact of recreational riding of off-highway vehicles on lizards. Thirty-six lizards, in situ, were treated with an off-highway vehicle treatment during hibernation season in three treatment groups: high impact, low impact, and control. Treatments consisted of timed riding by off-highway vehicles. In all treatment groups survival was 100%, despite hibernation of lizards at very shallow depths. Consequently, indirect effects of off-highway vehicles deserve increased attention. The relative importance of direct versus indirect (i.e., degradation of lizard habitat) impacts caused by off-highway vehicles remains unknown. These indirect effects may include the altering of vegetation, substrate, and prey. We recommend that a manipulative approach be adopted to investigate these possibilities.
authors.affiliation: Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 50823-1474, USA. Tyler_Grant@fws.gov
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Grant
authors.forename: Paul F
authors.initials: PF
authors.lastname: Doherty
mesh_terms: D000059:Accidents; D000818:Animals; D002140:California; D003247:Conservation of Natural Resources; D008116:Lizards / Q000254:growth & development*; D015541:Off-Road Motor Vehicles; D011156:Population Density; D011998:Recreation; D014186:Transportation